1. Field of the Invention
The present invention is directed to a method and an arrangement for locating a measurement and/or a treatment catheter in a vessel or an organ of a patient, wherein signals are transmitted (emitted) by one of these catheters, the signals being used to locate the position of the catheter which transmitted the signals.
2. Description of the Prior Art
For many medical applications it is desirable to be able to locate a catheter in a patient, e.g. in angiographic examinations and in cardiac diagnostics and therapy.
Thus, U.S. Pat. No. 5,042,486 describes a method for real time portrayal of a catheter in a vessel, which makes use of a transmitter for electromagnetic or acoustic waves located at the tip of the catheter. These waves are received by receiving antennas attached to the exterior surface of the patient and are converted into electrical image signals. From these signals the position of the catheter relative to external antennas is determined. A disadvantage of this technique is that the patient may not flex or bend or even breathe since the external antennas will then move relative to each other and to the catheter and the information will be distorted and the results unreliable and inaccurate. In U.S. Pat. Nos. 5,391,199 and 5,443,489 apparatuses and methods for treating cardiac arrhythmias and for ablation are described. Reference catheters, having a receiving or sending antenna, are then introduced into the heart and the position of a mapping/ablating catheter relative the reference catheters is determined by use of an external transmitter or receiver. The primary image of the structure studied, e.g. the heart, upon which a catheter map is superimposed, is obtained by an appropriate method, such as by x-ray imaging. By using fixed catheters the accuracy of location is improved and the correct orientation and superposition of the vessel image and the catheter location map is facilitated. If three or more fixed reference catheters, introduced into the heart, are used, it is possible for the patient to move and breathe freely without impairing the results. It is thus possible to have the external antennas fixed relative to the room, and not necessary to have them fixed relative the patient. However, the use of external antennas for transmitting electromagnetic fields for this purpose is associated with difficulties when the patient is lying in a bed and if ultrasonic waves are used the patient should preferably be immersed in water to obtain a satisfactory signal transmission between the exterior and the interior of the patient. Thus, this technique is complicated and impractical.